Magnetic fields, while ubiquitous in many astrophysical environments, are challenging to measure observationally. Based on the properties of anisotropy of eddies in magnetized turbulence, the velocity gradient technique is a method synergistic to dust polarimetry that is capable of tracing plane-of-the-sky magnetic fields, measuring the magnetization of interstellar media and estimating the fraction of gravitational collapsing gas in molecular clouds using spectral line observations. Here, we apply this technique to five low-mass star-forming molecular clouds in the Gould Belt and compare the results to the magnetic field orientation obtained from polarized dust emission. We find that the estimates of magnetic field orientations and magnetization for both methods are statistically similar. We estimate the fraction of collapsing gas in the selected clouds. By using the velocity gradient technique, we also present the plane-of-the-sky magnetic field orientation and magnetization of the Smith Cloud, for which dust polarimetry data are unavailable. The velocity gradient technique is used to measure the magnetic field orientations and magnetization of five low-mass star-forming molecular clouds, also finding that collapsing regions constitute a small fraction of the volume in these clouds.

Magnetic field morphology in interstellar clouds with the velocity gradient technique

Fermi has been instrumental in constraining the luminosity funct ion and redshift evolution of gamma-ray bright blazars. Thi s includes limits upon the spectrum and anisotropy of the extragalactic gamma-ray background (EGRB), redshift distribution of nearby Fermi active galactic nuclei (AGN), and the construction of a logN -log S relation. Based upon these, it has been argued that the evolution of the gamma-ray bright blazar population must be much less dramatic than that of other AGN. However, critical to such claims is the assumption that inverse Compton cascades reprocess emission above a TeV into the Fermi energy range, substantially enhancing the strength of the observed limits. Here we demonstrate that in the absence of such a process, due, e.g., to the presence of virulent plasma beam instabilities that preempt the casc ade, a population of TeV-bright blazars that evolve similar ly to quasars is consistent with the population of hard gamma-ray blazars observed by Fermi. Specifically, we show that a simple model for the properties and luminosity function is simultaneously a ble to reproduce their logN -log S relation, local redshift distribution, and contribution to the EGRB and its anisotropy without any free parameters. Insofar the naturalness of a picture in which the hard gamma-ray blazar population exhibits the strong redshift evolution observed in other tracers of the cosmological hist ory of accretion onto halos is desirable, this lends support for the absence o f the inverse Compton cascades and the existence of the beam plasma instabilities. Subject headings:BL Lacertae objects: general ‐ gamma rays: general ‐ radiation mechanisms: non-thermal

http://iopscience.iop.org/article/10.1088/0004-637X/790/2/137/pdf

Implications of Plasma Beam Instabilities for the Statistics of the Fermi Hard Gamma-Ray Blazars and the Origin of the Extragalactic Gamma-Ray Background

The origin of the near-infrared (NIR) HI emission lines in young stellar objects are not yet understood. To probe it, we present multi-epoch LBT-LUCIFER spectroscopic observations of the Pa{\delta}, Pa{\beta}, and Br{\gamma} lines observed in the Herbig star VVSer, along with VLTI-AMBER Br{\gamma} spectro-interferometric observations at medium resolution. Our spectroscopic observations show line profile variability in all the HI lines. The strongest variability is observed in the redshifted part of the line profiles. The Br{\gamma} spectro-interferometric observations indicate that the Br{\gamma} line emitting region is smaller than the continuum emitting region. To interpret our results, we employed radiative transfer models with three different flow configurations: magnetospheric accretion, a magneto-centrifugally driven disc wind, and a schematic bipolar outflow. Our models suggest that the HI line emission in VVSer is dominated by the contribution of an extended wind, perhaps a bipolar outflow. Although the exact physical process for producing such outflow is not known, this model is capable of reproducing the averaged single-peaked line profiles of the HI lines. Additionally, the observed visibilities, differential and closure phases are best reproduced when a wind is considered. Nevertheless, the complex line profiles and variability could be explained by changes in the relative contribution of the magnetosphere and/or winds to the line emission. This might indicate that the NIR HI lines are formed in a complex inner disc region where inflow and outflow components might coexist. Furthermore, the contribution of each of these mechanisms to the line appears time variable, suggesting a non-steady accretion/ejection flow.

Investigating the origin and spectroscopic variability of the near-infrared H I lines in the Herbig star VV Ser

We present the results from a study of nitrogen chemistry in Class 0/I proto-brown dwarfs (proto-BDs). We have used the IRAM 30 m telescope to observe the CN (2-1), HCN (3-2), and HNC (3-2) lines in seven proto-BDs. All proto-BDs show a large CN/HCN abundance ratio of >20, and an HNC/HCN abundance ratio close to or larger than unity. The enhanced CN/HCN ratios can be explained by high UV flux originating from an active accretion zone in the proto-BDs. The larger than unity HNC/HCN ratio for the proto-BDs is likely caused by a combination of low temperature and high density. Both CN and HNC show a flat distribution with CO, indicating that these species can survive in regions where CO is depleted. We have investigated the correlations in the molecular abundances of these species for the proto-BDs with Class 0/I protostars. We find tentative trends of CN (HCN) abundances being about an order of magnitude higher (lower) in the proto-BDs compared to protostars. HNC for the proto-BDs shows a nearly constant abundance unlike the large spread of similar to 2 orders of magnitude seen for the protostars. Also notable is a rise in the HNC/HCN abundance ratio for the lowest luminosity objects, suggesting that this ratio is higher under low-temperature environments. None of the relatively evolved Class Flat/Class II brown dwarfs in our sample show emission in HNC. The HNC molecule can be considered as an efficient tracer to search and identify early-stage sub-stellar mass objects.

Chemical tracers in proto-brown dwarfs: CN, HCN, and HNC observations

The Serpens filament, as one of the nearest infrared dark clouds, is regarded as a pristine filament at a very early evolutionary stage of star formation. In order to study its molecular content and dynamical state, we mapped this filament in seven species: (CO)-O-18, HCO+, HNC, HCN, N2H+, CS, and CH3OH. Among them, HCO+, HNC, HCN, and CS show self-absorption, while (CO)-O-18 is most sensitive to the filamentary structure. A kinematic analysis demonstrates that this filament forms a velocity-coherent (trans) sonic structure, a large part of which is one of the most quiescent regions in the Serpens cloud. Widespread (CO)-O-18 depletion is found throughout the Serpens filament. Based on the Herschel dust-derived H-2 column density map, the line mass of the filament is 36-41 M-circle dot pc(-1), and its full width at half maximum is 0.17 +/- 0.01 pc, while its length is approximate to 1.6 pc. The inner radial column density profile of this filament can be well fitted with a Plummer profile with an exponent of 2.2 +/- 0.1, a scale radius of 0.018 +/- 0.003 pc, and a central density of (4.0 +/- 0.8) x 10(4) cm(-3). The Serpens filament appears to be slightly supercritical. The widespread blue-skewed HNC and CS line profiles and HCN hyperfine line anomalies across this filament indicate radial infall in parts of the Serpens filament. (CO)-O-18 velocity gradients also indicate accretion flows along the filament. The velocity and density structures suggest that such accretion flows are likely due to a longitudinal collapse parallel to the filament's long axis. Both the radial infall rate (similar to 72 M-circle dot Myr(-1), inferred from HNC and CS blue-skewed profiles) and the longitudinal accretion rate (similar to 10 M-circle dot Myr(-1), inferred from (CO)-O-18 velocity gradients) along the Serpens filament are lower than all previously reported values in other filaments. This indicates that the Serpens filament lies at an early evolutionary stage when collapse has just begun, or that thermal and nonthermal support are effective in providing support against gravity.

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The Serpens filament at the onset of slightly supercritical collapse

We mapped 12CO and 13CO J = 2-1 emission over 1.04 deg2 of the Serpens molecular cloud with 38'' spatial and 0.3 km s–1 spectral resolution using the Arizona Radio Observatory Heinrich Hertz Submillimeter Telescope. Our maps resolve kinematic properties for the entire Serpens cloud. We also compare our velocity moment maps with known positions of young stellar objects (YSOs) and 1.1 mm continuum emission. We find that 12CO is self-absorbed and 13CO is optically thick in the Serpens core. Outside of the Serpens core, gas appears in filamentary structures having LSR velocities which are blueshifted by up to 2 km s–1 relative to the 8 km s–1 systemic velocity of the Serpens cloud. We show that the known Class I, flat, and Class II YSOs in the Serpens core most likely formed at the same spatial location and have since drifted apart. The spatial and velocity structure of the 12CO line ratios implies that a detailed three-dimensional radiative transfer model of the cloud will be necessary for full interpretation of our spectral data. The "starless cores" region of the cloud is likely to be the next site of star formation in Serpens.

http://iopscience.iop.org/article/10.1088/0067-0049/209/2/39/pdf

A. Chromey

Papers

The arizona radio observatory co mapping survey of galactic molecular clouds. iii. the serpens cloud in co j = 2-1 and 13co j = 2-1 emission